SAN FRANCISCO (Reuters) - Facebook Inc Chief Executive Mark Zuckerberg on Tuesday ordered one of the biggest management shakeups in the history of the social network, giving more responsibility to his chief product officer and launching a blockchain division.

Blockchain = Bitcoin. Facebook is no doubt mining Bitcoin now. Bitcoin was invented by a rather eccentric Japanese man who is maybe in his sixties, carries a purse, and lives with his mother. A large quantity of Bitcoin, that is, a large fraction of all extant Bitcoin from its earliest inception is still owned by the founders of the cryptocurrency scheme. The Bitcoin scheme uses an iterated SHA256 hash as "proof of work" to secure the entire system.

possible values. Theoretically, in an asymptotic sense, assuming "perfect" or "near-ideal" mathematical properties of the hash, each iteration reduces its event space by an approximate factor of 1-1/e, or about 0.63212. This is equivalent to a reduction of 0.6617284 bits for each iteration of the hash.

Thus a 256-bit hash is reduced in strength to 255.3383 bit simply by performing a second iteration on it. Iterating a 256-bit hash some 387 times would in theory be sufficient to asymptotically deplete the information-theoretic entropy of its event space to zero.

As the blocks are "chained," I am suspecting that the effect of information-theoretic entropy depletion due to the iteration inherent in the chaining allows older transactions to be reversed, altered, and forged.